If you are self-employed (a freelancer, contractor or sole trader), you report your trading income on the SA103 supplementary pages that form part of your HMRC Self Assessment tax return.
The SA103 pages are the self-employment supplement of the Self Assessment return. They are used by individual sole traders — freelancers, contractors and people running their own business — to tell HMRC how much profit they made in the tax year. You need them if you traded in the UK or abroad as a self-employed individual in the year, even if the business made a loss or did not trade for the whole year. If you also receive rental income, that goes on the SA105 UK Property pages instead, or alongside. If you run your business through a limited company, you are not self-employed for tax purposes and the SA103 is not for you — the company's profits are handled separately through corporation tax and your own salary or dividends on your personal Self Assessment if you need to declare them.
You can deduct expenses from your trading income to arrive at your taxable profit, but there are two ways: you can claim your actual allowable expenses, or you can claim the £1,000 trading allowance for a tax year. You use whichever gives the higher deduction — you cannot claim both for the same income. The trading allowance is a flat £1,000 per tax year that can cover income from self-employment, casual income, or letting property or land (the property element is separate from your normal UK property letting). If your gross income is £1,000 or less, the allowance means you have no tax to pay on it. If you claim the trading allowance, you cannot also claim expenses for the same business.
You can deduct expenses that are incurred wholly and exclusively for the purposes of your business. Common examples for freelancers and contractors include office costs like rent and rates (or a portion of your home costs if you work from home), stationery and postage, travel, phone and internet, and professional fees such as accountancy fees. You can also claim a proportion of your costs for things you use partly for business and partly privately, like a mobile phone. You cannot deduct the cost of anything that is not for your business, or any private element of mixed-use purchases. Things used to buy capital items for the business — like equipment — are not running expenses but can qualify for capital allowances instead. Keep records of every expense so you can substantiate what you claim.
KAZAALBAIDA gives self-employed freelancers a single place to track turnover and expenses throughout the year, categorised against the allowable expense rules, so you have organised, consistent totals when Self Assessment comes around. Logging expenses as you go means fewer missed deductions and no last-minute receipt hunting. The platform estimates your income tax, Class 2 and Class 4 National Insurance and whether you will need to make payments on account, and generates a pre-filled SA103-style summary you can use as the basis for your return.
SA103 UK freelance guide: reporting self-employment profit on your Self Assessment return, allowable expenses, and HMRC deadlines 2025/26.
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